Process for controlling the polishing process of an optical element

ABSTRACT

The invention concerns a process for measuring and/or controlling a polishing process of an ophthalmic element ( 1 ) comprising the steps of
         manufacturing at least two cavities ( 2, 3 ) on the surface of the element to be polished, the depth of the first cavity ( 2 ) being smaller than the depth of the second cavity ( 3 )   operating the polishing process   considering the element ( 1 ), in order to check that the first cavity ( 2 ) is suppressed and that the second cavity ( 3 ) is present.

The invention relates to a process for controlling the polishing processof an optical element, such an ophthalmic lens.

In this text, the word “polishing” is meaning in fact the smoothing andthe polishing per se. The smoothing consists to suppress material on adepth comprised between 50 and 200 microns, and, after smoothing, thepolishing per se consists to suppress material on a depth comprisedbetween 3 and 50 microns.

Ophthalmic lenses require high quality standard, therefore high qualitymanufacturing process is to be used in order to obtain high qualityophthalmic lenses.

Cast molding requires the use of two complementary molds in which thelens material is added by gravity casting. These molds present aspecific design corresponding to the desired lens design. Therefore, newmanufacturing techniques including cutting specially digital surfacingand polishing steps are used.

In the art of lens manufacture, a finished lens is usually made from asemi-finished lens blank by using new technologies like digitalsurfacing. Semi-finished lens blanks have usually optically finishedfront surfaces. Then, they are cut, polished and coated to producefinished uncut lenses. Finished uncut lenses are then edged to theproper frontal shape and edge contour to fit into spectacle/glassesframes or other mounting structures.

To generate a desired prescription for a lens, calculations are requiredto determine the topography of the surfaces of the lens, namely its backsurface if semi-finished lens blank is used, Such calculations typicallyinvolve variables that include the front surface radii of thesemi-finished blank, the index of refraction of the lens blank material,prescription values of the desired lens, statutory values regardingminimum lens thickness, and the physical dimensions of the frame ormounting structure.

After the appropriate accuracy and smoothness is achieved in the cuttingprocess, the surface is then polished and coated to produce a surface ofoptical quality. The optically finished lens is then edged to the propershape and edge profile to fit into or with the frame for which the lenswas made.

Today there are processes for controlling the process of manufacturing,but these processes do not permit to control easily the polishingquality. When the lens presents a defect, it is difficult to detail, ifthe defect comes from the cutting process or from the polishing process.

Indeed, in spite of the use of a detailed process of polishing, theperformances of polishing can change in the time because of theadjustment of the operator, the conditions of the polishing bathes andthe ambient temperature.

It could be planned to control the polishing process with a 3D measuringmachine, but such machine is a heavy, complex and long working systemwhich is not compatible with the production means.

The goal of the present invention is to provide a mechanical process forcontrolling the polishing process of an optical element, specially anophthalmic lens or an ophthalmic mold, which is efficient, simple andrapid to use in workstation.

The invention relates to a process for measuring and/or controlling apolishing process of an ophthalmic element comprising the steps of

-   -   manufacturing at least two cavities on the surface of the        element to be polished, the depth of the first cavity being        smaller than the depth of the second cavity    -   operating the polishing process    -   considering the element, in order to check that the first cavity        is suppressed and that the second cavity is present.

By ophthalmic element, it is understood ophthalmic lens or ophthalmicmold.

According to a first preferred embodiment, the process for controlling apolishing process of an ophthalmic element comprises the steps of:

-   -   predetermining the reference value of the depth of the material        to be suppressed by polishing,    -   manufacturing at least two cavities on the surface of the        element to be polished, the depth of the first cavity being        smaller than said reference value and the depth of the second        cavity being greater than said reference value, the difference        between the depths of the cavities and said reference value        being comprised between à 0.5 and 50 microns,    -   operating the polishing process,    -   considering the element, in order to check that the first cavity        is suppressed and that the second cavity is present.

Preferably, two sets of cavities are manufactured, the constant depth ofthe first set being smaller than said reference value and the constantdepth of the second set being greater than said reference value.

A plurality of cavities can be manufactured, with different depthsaccording to a predetermined increment.

Said pitch is preferably comprised between 0.5 and 10 microns,

Said cavities can be holes disposed according a regular geometric form.

In case of polishing of progressive lens or mold to manufacture it, saidcavities can be disposed in its near vision zone.

Said cavities are disposed in its far vision zone.

Said cavities are disposed in its progression corridor, between its farvision zone and its near vision zone.

Said cavities are grooves.

According to a second preferred embodiment, the process for measuring apolishing process of an ophthalmic element comprises the steps of:

-   -   choosing points on the surface of the element,    -   manufacturing a plurality of holes near each said point, each        hole of each plurality of holes having a different depth with a        increment equal to the searched precision,    -   operating a controlled polishing process,    -   considering the element, in order to determine the polished        depth at each said point.

Non limited embodiments of the invention will now be described withreference to the accompanying drawings.

FIGS. 1 and 2 are views in vertical section of an ophthalmic element,illustrating a first embodiment the process according to the invention.

FIGS. 3 and 4 are front views of an ophthalmic element, illustrating asecond embodiment of the process according to the invention.

FIG. 5 is a front view of progressive ophthalmic lens, illustrating athird embodiment of the process according to the process according tothe invention.

The FIG. 6 is a view in vertical section of an ophthalmic element.

FIGS. 7 to 9 are front views of an ophthalmic element, illustrating aprocess of measuring a polishing process, according to the invention.

The process for controlling a polishing process of a surfaced ophthalmicelement 1 comprising the steps of:

-   -   predetermining the reference value X of the depth of the        material to be suppressed by polishing, the reference value of        smoothing being comprised between 50 and 200 microns and the        reference value of polishing per se being comprised between 3        and 50 microns,    -   manufacturing at least two micro-holes 2, 3, with a diameter        comprised between 10 and 100 microns, on the surface of the        element to be polished, the depth of the first hole 2 being        smaller than the reference value X and the depth of the second        hole 3 being greater than the reference value X, the difference        between the depths of the holes 2, 3 and said reference value X        being comprised between à 0.5 and 50 microns, as illustrated in        FIG. 1,    -   operating the smoothing or polishing process,    -   considering the element 1, in order to check that the first hole        2 is suppressed and that the second hole 3 is present, as        illustrated in FIG. 2.

In fact, on FIG. 1, two sets of holes S₁, S₂ are manufactured, theconstant depth of the first set S₁, for example three holes 2, beingsmaller than the reference value X and the constant depth of the secondset S₂, for example two holes 3, being greater than the reference valueX.

For a preferred example, appropriated to ophthalmic lens or toophthalmic mold, the reference value is comprised between 15 and 20microns and the depth of the first holes 2 is equal to 15 microns andthe depth of the second holes 3 is equal to 20 microns.

According to this first embodiment of the invention, as represented, theprocess of controlling permit to check that the depth of the materialsuppressed by polishing is effectively comprised between 15 and 20microns. In other case, if some second holes 3 are suppressed or if somefirst holes 2 are always present, the polishing process presents adefect.

The precision of the controlling can be increased by manufacturing of aplurality of holes, with different depths according to a predeterminedincrement, preferably comprised between 0.5 and 10 microns.

The holes can be advantageously linear grooves, preferably disposedaccording a regular geometric form, for example according to concentriccircles, squares or diameters. They could present specific sections, forexample with form of cross, in order to be differentiated easily.

The FIG. 3 illustrates such second embodiment, where the surface have arevolution symmetry and where a plurality of holes G_(i) is manufacturedaccording to several radius, associated to a set of constant distancesto the center of the ophthalmic element, with different depths accordingto a predetermined increment, for example equal to 1 micron.

After polishing, the element is as illustrated in the FIG. 4, thepresent holes demonstrate that the polishing is not uniform and that thequantity of material suppressed by polishing is smaller in the vicinityof the edges of the element and higher in the vicinity of the centre ofthe element.

Preferably, the controlling is made in critical places of the ophthalmicelement.

The FIG. 5 illustrates such case of a progressive ophthalmic lens.

Advantageously, the holes or the grooves can be disposed in its nearvision zone and/or in its far vision zone.

The holes or the grooves G_(i) are disposed in the progression corridorPW, between the far zone and the near zone of the lens.

In the represented example in FIG. 5, other grooves G_(i)′ are disposedin concentric circles too.

The holes or grooves can be manufactured by means of a laser ormechanically. They can be manufactured directly in the generating orcutting machine.

The final determination of the subsisting holes or grooves can be madeby a simple visualization, by means of an arc lamp in reflective ortransmissive mode or by means of a camera.

The process according to the invention can be applied to an ophthalmiclens or to a mold to manufacture it.

The preferred embodiments of the process according to the invention havebeen described here above.

The invention concerns also a more basic process that comprises thesteps of:

-   -   predetermining the reference value X of the depth of the        material to be suppressed by polishing,    -   manufacturing only one micro-hole 2 or 3 or only one set of        micro-holes S₁ or S₂ on the surface of the element to be        polished, the depth of the hole or the set of holes being        smaller than said reference value or being greater than said        reference value,    -   operating the polishing process,    -   considering the element 1, in order to check that the hole 2 or        3 or the set of holes S₁ or S₂ is suppressed or present.

Although this embodiment of process does not give a complete control, itcan be applied in order to control the polishing in some specific cases,for example when the polishing is supposed to suppress a quantity ofmaterial too small or too great, or when the uniformity of the polishingis to control.

More generally, the reference value X of the depth p of the material tobe suppressed by polishing is not constant for one cut ophthalmicelement 1 and the invention proposes for measuring a polishing in orderto determine the reference surface L of polishing, as represented on theFIG. 6.

As detailed here above, this variable depth is comprised between 50 and200 microns for the step of smoothing and between 3 and 50 microns forthe step of polishing per se.

According to the invention, the process for measuring a polishingprocess of an ophthalmic element 1, for example in order to determinethe formed reference surface L, comprises the steps of:

-   -   choosing points P_(i) on the surface of the element 1,        preferable regularly distributed on the surface of the element,    -   manufacturing a plurality of micro-holes near each said point        P_(i), each hole MH_(j) of each plurality of holes having a        different depth with a increment equal to the searched        precision,    -   operating a controlled polishing process,    -   considering the element 1, in order to determine the polishing        depth at each said point P_(i).

According to a preferred embodiment illustrated on FIG. 7, the processto determinate the reference surface L consists to choose some pointsP_(i) on the cut element and to realise a plurality of micro-holesaround and in vicinity of these points. The number of holes is at leastequal to

1+higher natural value of [(maximal depth−minimal depth)/increment],

with maximal depth equal to 200 microns and minimal depth equal to 50microns, for smoothing,

with maximal depth equal to 50 microns and minimal depth equal to 3microns, for polishing per se.

For example, twenty holes can be made around each point. Each hole ofthis plurality of holes has a different depth from one micron to twentymicrons, with a regular increment equal to one micron.

The element is then polished with a correct and controlled process andaccording to the present holes, the reference value X in said points canbe defined with a precision of one micron, as illustrated on FIGS. 8 and9.

Such process can be used by repartition of each plurality of holes ofdifferent ophthalmic elements.

1. Process for measuring and/or controlling a polishing process of anophthalmic element comprising the steps of manufacturing at least twocavities on the surface of the element to be polished, the depth of thefirst cavity being smaller than the depth of the second cavity;operating the polishing process; and considering the element, in orderto check that the first cavity is suppressed and that the second cavityis present.
 2. Process for controlling a polishing process of anophthalmic element according to claim 1, comprising the steps of:predetermining the reference value (X) of the depth of the material tobe suppressed by polishing; manufacturing at least two cavities on thesurface of the element to be polished, the depth of the first cavitybeing smaller than said reference value and the depth of the secondcavity being greater than said reference value, the difference betweenthe depths of the cavities and said reference value (X) being comprisedbetween 0.5 and 50 microns; operating the polishing process; andconsidering the element, in order to check that the first cavity issuppressed and that the second cavity is present.
 3. Process accordingto claim 1, wherein two sets of cavities are manufactured, the constantdepth of the first set being smaller than said reference value and theconstant depth of the second set being greater than said referencevalue.
 4. Process according to claim 1, wherein a plurality of cavitiesis manufactured, with different depths according to a predeterminedincrement.
 5. Process according to claim 4, wherein said pitch iscomprised between 0.5 and 10 microns.
 6. Process according to claim 1,wherein said cavities are holes disposed according a regular geometricform.
 7. Process for controlling a polishing process of progressive lensor mold to manufacture said progressive lens, according to claim 1,wherein said cavities are disposed in a near vision zone of saidprogressive lens.
 8. Process for controlling a polishing process ofprogressive lens or mold to manufacture said progressive lens, accordingto claim 7, wherein said cavities are disposed in a far vision zone ofsaid progressive lens.
 9. Process for controlling a polishing process ofprogressive lens or mold to manufacture said progressive lens, accordingto claim 8, wherein said cavities are disposed in a progressioncorridor, between said far vision zone and said near vision zone of saidprogressive lens.
 10. Process according to claim 1, wherein saidcavities are grooves.
 11. Process for measuring a polishing process ofan ophthalmic element (1) according to claim 1, comprising the steps of:choosing points on the surface of the element; manufacturing a pluralityof holes near each said point, each hole of each plurality of holeshaving a different depth with a increment equal to the searchedprecision; operating a controlled polishing process; and considering theelement, in order to determine the polished depth at each said point.